The present invention relates to a distance-measuring system for measuring a distance to an object by using a laser beam.
In recent years, a non-prism distance-measuring system, a distance to an object to be measured is measured by directly projecting a laser beam for distance measurement to the object to be measured.
In the non-prism distance-measuring system, a laser beam with a smaller beam diameter is used. By using the laser beam with a smaller beam diameter, the laser beam can be projected to the object to be measured by pinpoint. A measuring position on the object can be clearly defined, and it is possible to measure a crest line or a specific point of the object to be measured.
Because an intensity of the projected laser beam is limited from reasons such as safety, in the non-prism distance measuring system, in which high reflection from the object to be measured cannot be expected, the measured distance is shorter compared with a distance-measuring system using a prism (corner cube).
For this reason, a prism is used as the object to be measured in long-distance measurement. Also, a laser beam having a relatively large beam spreading is used to facilitate collimation and to achieve measurement with high accuracy.
As described above, the beam diameter of the laser beam is small in the non-prism distance-measuring system, and it is difficult to project the laser beam to the prism. Accordingly, this is not suitable for the measurement of long distance by using a prism.
However, it is not very economical to provide a distance-measuring system for long distance using a prism and a non-prism distance-measuring system. In this respect, it is proposed now to have a distance-measuring system, in which it is possible to carry out distance-measurement using a prism and non-prism distance-measurement in a single distance-measuring system.
For instance, a distance-measuring system is proposed as described in JP-A-2000-88566 (FIG. 1, and paragraphs [0029]–[0035]), in which distance-measurement using a prism and distance-measurement on non-prism basis can be carried out by a single distance-measuring system.
Referring to FIG. 6, brief description will be given below.
There are provided a first light source 2 for emitting a visible laser beam 1 and a second light source 4 for emitting an infrared laser beam 3. The visible laser beam 1 and the infrared laser beam 3 are emitted independently from each other. The visible laser beam 1 is a laser beam of parallel luminous fluxes with a small beam diameter, and the infrared laser beam 3 is a divergent laser beam.
The visible laser beam 1 or the infrared laser beam 3 is selected depending upon the object to be measured. For instance, in case an object to be measured 5 is a reflector such as a corner cube, the divergent infrared laser beam 3 is projected. In case the object to be measured 5 is a wall surface of a building, etc., the visible laser beam 1 with a small beam diameter is projected. A reflected light 11 from the object to be measured 5 is received by a detector 8 through an objective lens 6 and a filter 7. Based on a signal from the detector 8, a distance to the object to be measured 5 can be measured by an arithmetic operation unit 12.
The filter 7 transmits only wavelength ranges of the visible laser beam 1 and the infrared laser beam 3. Unnecessary light such as sunlight is cut off to improve detection accuracy of the detector 8 to detect the reflection light 11.
In the conventional system as described above, two light sources are used, and this requires a complicated light emitting unit for controlling the light sources, etc. Also, the visible laser beam 1 and the infrared laser beam 3 are used, and the filter 7 must cope with wavelength ranges of the two laser beams, and this means that higher cost is involved.